Fine-tuned Universe

The fine-tuned Universe is the proposition that the conditions that allow life in the Universe can only occur when certain universal fundamental physical constants lie within a very narrow range, so that if any of several fundamental constants were only slightly different, the Universe would be unlikely to be conducive to the establishment and development of matter, astronomical structures, elemental diversity, or life as it is understood.[1] The proposition is discussed among philosophers, scientists, theologians, and proponents and detractors of creationism.

Physicist Paul Davies has asserted that "There is now broad agreement among physicists and cosmologists that the Universe is in several respects ‘fine-tuned' for life". However, he continues, "the conclusion is not so much that the Universe is fine-tuned for life; rather it is fine-tuned for the building blocks and environments that life requires." He also states that "'anthropic' reasoning fails to distinguish between minimally biophilic universes, in which life is permitted, but only marginally possible, and optimally biophilic universes, in which life flourishes because biogenesis occurs frequently".[2] Among scientists who find the evidence persuasive, a variety of natural explanations have been proposed, such as the anthropic principle along with multiple universes. George F. R. Ellis observes "that no possible astronomical observations can ever see those other universes. The arguments are indirect at best. And even if the multiverse exists, it leaves the deep mysteries of nature unexplained."[3]

In 1913, the chemistLawrence Joseph Henderson (1878–1942) wrote The Fitness of the Environment, one of the first books to explore concepts of fine tuning in the Universe. Henderson discusses the importance of water and the environment with respect to living things, pointing out that life depends entirely on the very specific environmental conditions on Earth, especially with regard to the prevalence and properties of water.[4]

John Gribbin and Martin Rees wrote a detailed history and defence of the fine-tuning argument in their book Cosmic Coincidences (1989). According to Gribbin and Rees, carbon-based life was not haphazardly arrived at, but the deliberate end of a Universe "tailor-made for man."[8][page needed]

The premise of the fine-tuned Universe assertion is that a small change in several of the dimensionlessfundamental physical constants would make the Universe radically different. As Stephen Hawking has noted, "The laws of science, as we know them at present, contain many fundamental numbers, like the size of the electric charge of the electron and the ratio of the masses of the proton and the electron. ... The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life."[9]

If, for example, the strong nuclear force were 2% stronger than it is (i.e., if the coupling constant representing its strength were 2% larger), while the other constants were left unchanged, diprotons would be stable and hydrogen would fuse into them instead of deuterium and helium.[10] This would drastically alter the physics of stars, and presumably preclude the existence of life similar to what we observe on Earth. The existence of the diproton would short-circuit the slow fusion of hydrogen into deuterium. Hydrogen would fuse so easily that it is likely that all of the Universe's hydrogen would be consumed in the first few minutes after the Big Bang.[10] However, some of the fundamental constants describe the properties of the unstable strange, charmed, bottom and top quarks and mu and tau leptons that seem to play little part in the Universe or the structure of matter.[citation needed]

The precise formulation of the idea is made difficult by the fact that physicists do not yet know how many independent physical constants there are. The current standard model of particle physics has 25 freely adjustable parameters with an additional parameter, the cosmological constant, for gravitation. However, because the standard model is not mathematically self-consistent under certain conditions (e.g., at very high energies, at which both quantum mechanics and general relativity are relevant), physicists believe that it is underlaid by some other theory, such as a grand unified theory, string theory, or loop quantum gravity. In some candidate theories, the actual number of independent physical constants may be as small as one. For example, the cosmological constant may be a fundamental constant, but attempts have also been made to calculate it from other constants, and according to the author of one such calculation, "the small value of the cosmological constant is telling us that a remarkably precise and totally unexpected relation exists among all the parameters of the Standard Model of particle physics, the bare cosmological constant and unknown physics."[11]

Epsilon (ε), the strength of the force binding nucleons into nuclei, is 0.007. If it were 0.006, only hydrogen could exist, and complex chemistry would be impossible. If it were 0.008, no hydrogen would exist, as all the hydrogen would have been fused shortly after the big bang.[12]

Omega (Ω), also known as the Density parameter, is the relative importance of gravity and expansion energy in the Universe. It is the ratio of the mass density of the Universe to the "critical density" and is approximately 1. If gravity were too strong compared with dark energy and the initial metric expansion, the Universe would have collapsed before life could have evolved. On the other side, if gravity were too weak, no stars would have formed.[12]

Lambda (λ) is the cosmological constant. It describes the ratio of the density of dark energy to the critical energy density of the Universe, given certain reasonable assumptions such as positing that dark energy density is a constant. In terms of Planck units, and as a natural dimensionless value, the cosmological constant, λ, is on the order of 10−122.[13] This is so small that it has no significant effect on cosmic structures that are smaller than a billion light-years across. If the cosmological constant was not extremely small, stars and other astronomical structures would not be able to form.[12]

Q, the ratio of the gravitational energy required to pull a large galaxy apart to the energy equivalent of its mass, is around 10−5. If it is too small, no stars can form. If it is too large, no stars can survive because the Universe is too violent, according to Rees.[12]

D, the number of spatial dimensions in spacetime, is 3. Rees claims that life could not exist if there were 2 or 4.[12]

An older example is the Hoyle state, the third-lowest energy state of the carbon-12 nucleus, with an energy of 7.656 MeV above the ground level. According to one calculation, if the state's energy were lower than 7.3 or greater than 7.9 MeV, insufficient carbon would exist to support life; furthermore, to explain the Universe's abundance of carbon, the Hoyle state must be further tuned to a value between 7.596 and 7.716 MeV. A similar calculation, focusing on the underlying fundamental constants that give rise to various energy levels, concludes that the strong force must be tuned to a precision of at least 0.5%, and the electromagnetic force to a precision of at least 4%, to prevent either carbon production or oxygen production from dropping significantly.[14]

Physicist Victor Stenger objects to the fine-tuning, and especially to theist use of fine-tuning arguments. His numerous criticisms include what he calls "the wholly unwarranted assumption that only carbon-based life is possible."[15] In turn, the astrophysicist Luke Barnes has criticised much of Stenger's work.[16]

Fred Adams has investigated the existence of stars in universes with different values of the gravitational constantG, the fine-structure constantα, and a nuclear reaction rate parameter C. The study found that stars can exist in approximately 25% of the parameter space. His criteria of star existence is based on achieving sustained nuclear reaction and he suggests considering other factors, i.e. cosmic expansion, etc. in future work. The study addressed the question of whether stars can exist, not if life can exist -- asking the question about the life would introduce additional requirements that will place additional constraints.[17]

The fine-tuned Universe argument has also been criticized as an argument by lack of imagination, as it assumes no other forms of life, sometimes referred to as carbon chauvinism. Conceptually, alternative biochemistry or other forms of life are possible.[19] Regarding this, Stenger argues: "We have no reason to believe that our kind of carbon-based life is all that is possible. Furthermore, modern cosmology theorises that multiple universes may exist with different constants and laws of physics. So, it is not surprising that we live in the one suited for us. The Universe is not fine-tuned to life; life is fine-tuned to the Universe."[20]

In addition, critics argue that humans are adapted to the Universe through the process of evolution, rather than the Universe being adapted to humans (see puddle thinking, below). They also see it as an example of the logical flaw of hubris or anthropocentrism in its assertion that humans are the purpose of the Universe.[21]

There are fine tuning arguments that are naturalistic.[22][page needed] As modern cosmology developed, various hypotheses have been proposed. One is an oscillatory universe or a multiverse, where fundamental physical constants are postulated to resolve themselves to random values in different iterations of reality.[23] Under this hypothesis, separate parts of reality would have wildly different characteristics. In such scenarios, the issue of fine-tuning does not arise at all, as only those "universes" with constants hospitable to life (such as what we observe) would develop life capable of contemplating the question of the origin of fine-tuning.

Inflation theory posits that an inflaton field in the first 10−30 seconds of the Universe produces strong repulsive gravity, and the Universe and space-time expand by a factor of 1030. After 10−30 seconds, gravity starts to become attractive. In this framework, with such rapid expansion, the overall shape of the Universe at 14 billion years is much less sensitive to initial parameters than the standard big bang model, and thus the fine-tuning issue disappears.[24][citation needed]

The Multiverse hypothesis proposes the existence of many universes with different physical constants, some of which are hospitable to intelligent life (see multiverse: anthropic principle). Because we are intelligent beings, we are, by definition, in a hospitable universe.

This idea has led to considerable research into the anthropic principle and has been of particular interest to particle physicists, because theories of everything do apparently generate large numbers of universes in which the physical constants vary widely. As yet, there is no evidence for the existence of a multiverse, but some versions of the theory do make predictions that some researchers studying M-theory and gravity leaks hope to see some evidence of soon.[25] Some multiverse theories are not falsifiable, thus scientists may be reluctant to call any multiverse theory "scientific". UNC-Chapel Hill professor Laura Mersini-Houghton claims that the WMAP cold spot may provide testable empirical evidence for a parallel universe,[26] although this claim was recently refuted as the WMAP cold spot was found to be nothing more than a statistical artifact.[27] Variants on this approach include Lee Smolin's notion of cosmological natural selection, the Ekpyrotic universe, and the Bubble universe theory.

Critics of the multiverse-related explanations argue that there is no evidence that other universes exist.

According to this scenario, by means of a random quantum fluctuation, the Universe "tunneled" from pure vacuum ("nothing") to what is called a false vacuum, a region of space that contains no matter or radiation, but is not quite "nothing." The space inside this bubble of false vacuum was curved, or warped. A small amount of energy was contained in that curvature, somewhat like the energy stored in a strung bow. This ostensible violation of energy conservation is allowed by the Heisenberg uncertainty principle for sufficiently small time intervals. The bubble then inflated exponentially and the Universe grew by many orders of magnitude in a tiny fraction of a second. (For a not-too-technical discussion, see Stenger 1990[28]). As the bubble expanded, its curvature energy was converted into matter and radiation, inflation stopped, and the more linear Big Bang expansion we now experience commenced. The Universe cooled and its structure spontaneously froze out, as formless water vapor freezes into snowflakes whose unique patterns arise from a combination of symmetry and randomness.

In standard inflation, inflationary expansion occurred while the Universe was in a false vacuum state, halting when the Universe decayed to a true vacuum state. The bubble universe model proposes that different parts of this inflationary universe (termed a Multiverse) decayed at different times, with decaying regions corresponding to universes not in causal contact with each other. It further supposes that each bubble universe may have different physical constants.

Stephen Hawking, along with Thomas Hertog of CERN, proposed that the Universe's initial conditions consisted of a superposition of many possible initial conditions, only a small fraction of which contributed to the conditions we see today.[30] According to their theory, it is inevitable that we find our Universe's "fine-tuned" physical constants, as the current Universe "selects" only those past histories that led to the present conditions. In this way, top-down cosmology provides an anthropic explanation for why we find ourselves in a universe that allows matter and life, without invoking the existence of the Multiverse.[31]

One hypothesis is that the Universe may have been designed by extra-universal aliens. Some believe this would solve the problem of how a designer or design team capable of fine-tuning the Universe could come to exist. CosmologistAlan Guth believes humans will in time be able to generate new universes. By implication previous intelligent entities may have generated our Universe.[32] This idea leads to the possibility that the extraterrestrial designer/designers are themselves the product of an evolutionary process in their own universe, which must therefore itself be able to sustain life. However it also raises the question of where this universe came from, leading to an infinite regress.

The Designer Universe theory of John Gribbin suggests that the Universe could have been made deliberately by a member or members of a technologically advanced civilization in another part of the Multiverse, and that this advanced civilization may have been responsible for causing the Big Bang.[33]

Christian philosopher Alvin Plantinga argues that random chance, applied to a single and sole universe, only raises the question as to why this universe could be so "lucky" as to have precise conditions that support life at least at some place (the Earth) and time (within millions of years of the present).

One reaction to these apparent enormous coincidences is to see them as substantiating the theistic claim that the Universe has been created by a personal God and as offering the material for a properly restrained theistic argument—hence the fine-tuning argument. It's as if there are a large number of dials that have to be tuned to within extremely narrow limits for life to be possible in our Universe. It is extremely unlikely that this should happen by chance, but much more likely that this should happen, if there is such a person as God.

This fine-tuning of the Universe is cited[35] by philosopher and Christian apologist William Lane Craig as an evidence for the existence of God or some form of intelligence capable of manipulating (or designing) the basic physics that governs the Universe. Craig argues, however, "that the postulate of a divine Designer does not settle for us the religious question."

Theologian Alister McGrath has pointed out that the fine-tuning of carbon is even responsible for nature’s ability to tune itself to any degree.

[The entire biological] evolutionary process depends upon the unusual chemistry of carbon, which allows it to bond to itself, as well as other elements, creating highly complex molecules that are stable over prevailing terrestrial temperatures, and are capable of conveying genetic information (especially DNA). […] Whereas it might be argued that nature creates its own fine-tuning, this can only be done if the primordial constituents of the universe are such that an evolutionary process can be initiated. The unique chemistry of carbon is the ultimate foundation of the capacity of nature to tune itself.[37][38]

Theoretical physicist John Polkinghorne has stated: Anthropic fine tuning is too remarkable to be dismissed as just a happy accident.[39]

Mark Colyvan, Jay Garfield and Graham Priest (2005) have argued that a theistic explanation for fine tuning is faulted due to fallacious probabilistic reasoning.[40]

Mathematician Michael Ikeda and astronomer William H. Jefferys have argued that the anthropic principle and selection effect are not properly taken into account in the fine tuning argument for a designer, and that in taking them into account, fine tuning does not support the designer hypothesis.[41][42] Philosopher of science Elliott Sober makes a similar argument.[43]

Richard Carrier utilized the work of Ikeda, Jefferys, and Sober, in a Bayesian analysis. He concludes that fine tuning is strong evidence against the existence of God.[44][page needed]

Physicist Robert L. Park has also criticized the theistic interpretation of fine-tuning:

If the universe was designed for life, it must be said that it is a shockingly inefficient design. There are vast reaches of the universe in which life as we know it is clearly impossible: gravitational forces would be crushing, or radiation levels are too high for complex molecules to exist, or temperatures would make the formation of stable chemical bonds impossible... Fine-tuned for life? It would make more sense to ask why God designed a universe so inhospitable to life.[45]

Victor Stenger argues that "The fine-tuning argument and other recent intelligent design arguments are modern versions of God-of-the-gaps reasoning, where a God is deemed necessary whenever science has not fully explained some phenomenon".[15] Stenger argues that science may provide an explanation if a Theory of Everything is formulated, which he says may reveal connections between the physical constants. A change in one physical constant may be compensated by a change in another, suggesting that the apparent fine-tuning of the Universe is a fallacy because, in hypothesizing the apparent fine-tuning, it is mistaken to vary one physical parameter while keeping the others constant.[46]

Puddle theory is a term coined by Douglas Adams to satirize arguments that the Universe is made for man.[48][49] As stated in Adams's book The Salmon of Doubt:[50]

imagine a puddle waking up one morning and thinking, 'This is an interesting world I find myself in, an interesting hole I find myself in, fits me rather neatly, doesn't it? In fact, it fits me staggeringly well, must have been made to have me in it!' This is such a powerful idea that as the sun rises in the sky and the air heats up and as, gradually, the puddle gets smaller and smaller, it's still frantically hanging on to the notion that everything's going to be all right, because this World was meant to have him in it, was built to have him in it; so the moment he disappears catches him rather by surprise. I think this may be something we need to be on the watch out for.